The present invention relates to a ferromagnetic sputtering target that is used for the deposition of a magnetic thin film of a magnetic recording media, particularly for the deposition of a magnetic recording layer of a thermally assisted magnetic recording media, and to an FePt-based sintered sputtering target capable of achieving a stable discharge and reducing particle generation when sputtered with magnetron sputtering equipment.
In the field of magnetic recording mediums as represented with HDDs (hard disk drives), a material based on Co, Fe or Ni as ferromagnetic metals is being used as the material of a magnetic thin film which is used for the recording. For example, Co—Cr-based or Co—Cr—Pt-based ferromagnetic alloys containing Co as its main component are used for the recording layer of hard disks adopting the longitudinal magnetic recording system. Moreover, composite materials of Co—Cr—Pt-based ferromagnetic alloys containing Co as its main component and nonmagnetic inorganic grains are often used for the recording layer of hard disks adopting the perpendicular magnetic recording system which was recently put into practical application. In addition, a magnetic thin film of a magnetic recording medium such as a hard disk is often produced by sputtering a ferromagnetic sputtering target having the foregoing materials as its components in light of its high productivity.
Meanwhile, the recording density of magnetic recording mediums is rapidly increasing year by year, and the current surface density of 100 Gbit/in2 is expected to reach 1 Tbit/in2 in the future. When the recording density reaches 1 Tbit/in2, the size of the recording bit will fall below 10 nm. In such a case, it is anticipated that the superparamagnetization caused by thermal fluctuation will become a problem, and it is further anticipated that the currently used magnetic recording medium; for instance, a material with higher magnetic crystalline anisotropy obtained by adding Pt to a Co—Cr-based alloy, or a medium in which B is further added to the foregoing material to attenuate the magnetic coupling between the magnetic grains; will no longer be sufficient. This is because, for grains to stably behave ferromagnetically at a size of 10 nm or less, the grains need to possess even higher magnetic crystalline anisotropy.
In light of the above, an FePt phase having an L10 structure is attracting attention as a material for use in an ultrahigh density recording medium. Moreover, since an FePt phase having a L10 structure yields superior corrosion resistance and oxidation resistance, it is expected to become a material that can be suitably applied as a recording medium. The FePt phase has an order-disorder transformation point at 1573 K, and has a L10 structure even when an alloy is quenched from a high temperature due to the rapid ordered reaction. Furthermore, in connection with using the FePt phase as a material for use in an ultrahigh density recording medium, demanded is the development of technology for dispersing the ordered FePt phase, in a magnetically separated state, while densely aligning the orientation thereof as much as possible. In light of the foregoing circumstances, a magnetic thin film having a granular structure in which the FePt magnetic phase having an L10 structure is magnetically separated from each other through the interposition of nonmagnetic substances is being proposed for use in a magnetic recording medium of next-generation hard disks adopting the thermally assisted magnetic recording system.
This magnetic thin film having a granular structure has a structure in which the magnetic grains are magnetically insulated from each other through the interposition of nonmagnetic substances. The foregoing magnetic recording layer is configured from a magnetic phase such as a FePt alloy, and a nonmagnetic phase which is separating the magnetic phase, and it is known that C and BN are effective as a material of the nonmagnetic phase. When forming this kind of magnetic thin film, it is common to use an FePt alloy sputtering target containing C, rather than using multiple targets; that is, a C target and an FePt alloy target (for example, Patent Documents 1 and 2). Previously, the present inventors invented an FePt-based sputtering target containing C for forming a magnetic recording film (Patent Document 3), and an FePt-based sputtering target containing BN for forming a magnetic recording film (Patent Document 4).
An FePt-based sputtering target containing C or BN is normally prepared based on the powder sintering method. However, since the coefficient of thermal expansion of C or BN is too small relative to an FePt alloy, the compressive stress applied to C or BN increases as the sintering temperature becomes higher and, therefore, there were cases where C or BN would be subject to physical defects and cause particle generation during sputtering. Meanwhile, if the sintering temperature is too low, the density of the target will deteriorate, and there is a problem in that this would cause particle generation.